Natural Selection

- Variation is the fundamental starting point to the process of natural selection.
- If an environment changes, species have to evolve or they'll become extinct.

- Within a species, only the best-adapted individuals will survive.
→ We refer to them as 'survival of the fittest'.

- Survival of the fittest is part of the theory of natural selection, proposed by Charles Darwin in 1859.

Charles Darwin's Theory:

- Within a species, there's always natural genetic variation.
- Organisms produce more young than they will ever survive; there'll be competition for resources.
- Only the best adapted will survive.
- Those that survive to pass on their advantageous characteristics to their offspring.
- This happens over many generations.

- Many people objected to Darwin's theory when it was first published.
- This is it; it went against the teachings of the Church of England.
- Some people thought there wasn't enough evidence.
- Others disagreed: they thought God created all species individually.
- Some objected to the idea that humans may have evolved from apes.

Darwin vs. Lamarck

Darwin's Early Evidence:

- Darwin went to the Galapagos Islands (volcanic and geologically new).
- He realised that plants and animals must've arrived from the mainland.
- Many species were similar to mainland species, but none were the same and had changed over time.
- Darwin understood that species were malleable and subject to change.
- He began recording observations and gathering evidence for them.
- He explored finches and Galapagos tortoises on islands.
→ Darwin realised they had evolved.

- Darwin realised each island (the Galapagos) would have different selection pressures.
→ Selection pressures drive natural selection.
→ For instance, foxes may face selection pressure when they relocate to an area with rabbits, potentially leading to the emergence of a new species.
- Over time, a species can evolve into an entirely new one.
→ This necessitates the geographical and reproductive isolation of two populations.

- Species: A group of organisms that can interbreed to produce fertile offspring.

Peppered Moths

- In the early 19th century (before the Industrial Revolution), pepper-coloured moths were the most common phenotype, as they could camouflage better → less pollution.

- Over the next 50 years (Industrial Revolution), pollution increased; trees turned blacker.
→ Black moths increased and pepper-coloured moths decreased. Polluted trees provided better camouflage for black moths.

- Tutt proposed a hypothesis for this change.
- Kettlewell tested the hypothesis using a mark-release-recapture test; it proved the theory.
- To make evidence more repeatable, repeat it more.
- To make evidence more reproducible, ask someone else to carry out the same experiment.

Darwin's Observations Examples:

- Survival of the fittest → Hares with fur colour best suited to the environment survive.
- Competition for resources → Lynx are trying to find food, and hares are trying not to be eaten.
- Presence of natural variation → Hares are all born with slightly different-coloured fur.
- Inheritance of successful adaptations: Hares that survive pass on their genes for fur colour.

Speciation Example Answer

E.g., fish in a pond where water levels fall.
1. Different fish populations geographically isolate themselves when water levels fall.
2. If a mutation occurs in one population, it cannot spread to other populations.
3. Over many generations, genetic mutations accumulate.
4. Each separate population of fish will continue to evolve by natural selection.
5. This fish in different pods can become so genetically different that even when water levels rise again and they're not physically separated, they can no longer breed with the fish that were in other pools, as they are a different species.

Natural Selection Example Answer:

e.g., penguins
1. There is variation amongst the penguins.
2. Some penguins had more streamlined bodies than others.
3. There was competition between the two species.
4. More streamlined penguins were more likely to survive.
5. Streamlined is controlled by genes that are passed from one generation to another.
6. After many generations, enough differences may accumulate to form a new species.

- In a reproductive isolation Q, some animals won't be attracted to another type of that same animal → less mixing of genes → 2 species form from 1.